Monolithically integrated modulators (typically electroabsorption modulators) and lasers (typically distributed feedback/distributed Bragg reflector or DFB/DBR lasers) are known, and are expected to be key components of future long haul, high capacity optical fiber communication systems, due to their potentially low chirp and small DC drift, compactness and low drive voltage. Small chirp generally requires that essentially no reflection occurs at the output facet of the combination. Monolithically integrated modulator/laser combinations (I-MOD/DFB) are described, for instance, in M. Aoki et at., Electronics Letters, Vol. 29 (22), p. 1983; K. Suzuki et al., Electronics Letters, Vol. 29 (19), p. 1713; and P. I. Kuindersma et al., Electronics Letters, Vol. 29 (21), p. 1876. K. Sato et al., Proceedings of the European Conference on Optical Communications, 1993, weC7.2, disclose an I-MOD/DFB combination that comprises a multisection modulator portion, with a continuous multiquantum-well (MQW) layer extending the length of the combination, and a second MQW layer extending the length of the laser section only.
Prior art I-MOD/DFB combinations typically are designed to have an absorption layer in the modulator section that has a wider bandgap than the laser active medium, in order to avoid excessive absorption by the modulator when the modulator section is unbiased. Thus, the relevant layer or layers of prior art I-MOD/DFB combinations typically exhibits a variation of bandgap energy E.sub.g along the optical axis of the combination. Typically the reIevant layer (or layers) is a multi-quantum well (MQW) layer.
Recently it was discovered that the desired axial variation of E.sub.g can be attained by selective area growth by metalorganic vapor phase epitaxy (MOVPE), involving placement of axially oriented dielectric mask stripes on the relevant surface. The technique relies on the observation that in MOVPE the thickness (and typically the composition) of material grown in a region adjacent to a dielectric mask region is a function of the distance from the mask edge, and of the size of the mask region.
This discovery facilitates manufacture of I-MOD/DFB combinations. However, the process of designing and manufacturing such devices is still relatively complicated, requiting determination of the necessary mask geometry, mask formation, and close control of the MOVPE growth. In view of the significant potential of I-MOD/DFB combinations it would be desirable to have available such combinations that can be fabricated more easily, and that optionally can be relatively tolerant of output facet reflection. This application discloses such a I-MOD/DFB combination.